Micrometer tooth measuring apparatus

ABSTRACT

An apparatus for measuring the circumference of a tooth which includes a barrel, a sleeve rotatably positioned about the barrel in threaded engagement therewith, guide means positioned at a forward end of the barrel, and a doubled band slidably positioned within the guide means. The guide means includes an opening through which portions of the doubled band may extend in forming a closed loop. Means connect the band and sleeve such that axial movement of the sleeve is transmitted to the band while indicia on the barrel and sleeve denote the axial position of the sleeve with respect to the barrel. The size of the closed loop may be varied by rotation of the sleeve with respect to the barrel with the size of the loop being indicated by the indicia.

United States Patent Husted et al.

[ 51 June 17, 1975 1 MICROMETER TOOTH MEASURING APPARATUS [76] Inventors: Paul R. Husted, 201 Calle Miramar;

Felix Galan, 1935 Condon Ave, both of Redondo Beach, Calif. 90278 [22] Filed: Mar. 25, 1974 [211 Appl. No.: 454,756

[52] US. Cl. 33/179 [51] Int. Cl Glllb 3/10; GOlb 3/18 [58] Field of Search 33/179, 174 D, 176, 164 R; 32/14 A, 40 R, 63, 71

[56] References Cited UNITED STATES PATENTS 350.513 10/1886 Washburn 33/164 R 0,596.022 12/1897 Aber 33/179 0,744,358 11/1903 Kinsman 33/179 0,855,875 6/1907 Bode 33/179 0,861,874 7/1907 Macy 33/179 1233131 7/1917 Schwartz t i 33/179 1.361.376 12/1920 Fisher 33/179 2/1941 Hiirmann 33/179 6/1970 Ainsworth 32/63 [57] ABSTRACT An apparatus for measuring the circumference of a tooth which includes a barrel, a sleeve rotatably positioned about the barrel in threaded engagement therewith, guide means positioned at a forward end of the barrel, and a doubled band slidably positioned within the guide means. The guide means includes an opening through which portions of the doubled band may extend in forming a closed loop. Means connect the band and sleeve such that axial movement of the sleeve is transmitted to the band while indicia on the barrel and sleeve denote the axial position of the sleeve with respect to the barrel. The size of the closed loop may be varied by rotation of the sleeve with respect to the barrel with the size of the loop being indicated by the indicia.

12 Claims, 8 Drawing Figures PATENTEDJUN 17 1975 SHEET I MICROMETER TOOTH MEASURING APPARATUS BACKGROUND OF THE INVENTION In mounting orthodontic appliances within the mouth, the appliances are anchored in place through bands which are placed around teeth. The anchoring teeth may vary considerably in size depending upon whether they are molars, bicuspids, cuspids, etc., and also depending upon the size of the individual patients teeth.

Metal crowns may be used to protect a tooth which has been injured in some manner. Thus, for example, a crown may be placed over a childs tooth which has been injured to protect the tooth from decaying until the child and his teeth have developed and he is ready for repair of the tooth as an adult.

In the use of metal crowns in dentistry, there is a problem in determining the size of band or crown required by a particular tooth. Since there is no satisfactory means of measuring the teeth, the selection of the proper prefabricated band or crown is done by trial and error.

One means which has been used for measuring teeth prior to banding is to place a wire about a tooth to form a loop and to then measure the size of the loop. In forming a wire loop about the tooth being measured, the wire may, for example, be twisted until it is tightened about the tooth in forming a loop. The wire may then be removed and the loop measured.

In addition to being slow, the use of a wire in measuring teeth has not been satisfactory because the tooth may have an irregular exterior surface. Thus, the tooth dimension which is measured may not be the greatest circumferential dimension of the tooth. The wire may, for example, slide over the line of the greatest circumferential dimension and then be tightened about a smaller circumferential dimension to give an incorrect reading.

Since the greatest circumferential dimension is the dimension that determines the size of a band or crown needed for the tooth, it would be desirable if a measuring device could be provided which would consistently measure this distance rather than some smaller circumferential distance. In addition, it would be desirable if a measuring device could be provided which could be used in measuring teeth of all sizes and shapes ranging from the smallest to the largest of teeth. Lastly, it would be desirable if a measuring device could be provided which could be simply read in the manner of a micrometer.

SUMMARY OF THE INVENTION The present invention is directed to an apparatus for measuring the maximum circumference of a tooth in which the circumference is measured by a closed loop formed from a band having a sufficient height to extend over a substantial vertical portion of the tooth. Thus, the band will consistently measure the maximum circumferential distance about the tooth, even when the tooth has an irregular exterior surface.

The present apparatus employs a barrel with a sleeve rotatably positioned about the barrel in threaded engagement therewith. Guide means are positioned at a forward end of the barrel and a doubled band is slidably positioned within the guide means. The guide means includes an opening through which portions of the doubled band may extend in forming a closed loop. Means interconnect the band and the sleeve such that axial movement of the sleeve is transmitted to the band and indicia are provided on the barrel and sleeve to accurately denote the axial position of the sleeve with respect to the barrel. The size of the closed loop may, therefore, be varied by rotation of the sleeve with respect to the barrel with the circumference of the loop being read directly by the indicia on the barrel and sleeve.

Preferably the barrel is sufficiently long to permit a substantial axial movement of the sleeve with respect to the barrel. In this manner, the size of the loop may be varied to fit the entire size range of human teeth.

The guide means positioned at the forward end of the barrel may include a pair of guide arms, each having an inner end pivotally connected to the forward end of the barrel for pivotal movement of the arms away from each other to an open position. Interior guide surfaces for the doubled band may be defined on opposed portions of the guide arms with releasable means to fix the position of the arms in a closed position with the opposed portions in contacting relation with the doubled band slidably retained within the interior guide surfaces.

The interior guide surfaces may include a groove formed on each of the opposed portions of the guide arms. With the quide arms in closed position, the grooves may then form an enclosed guide passage for the doubled band. An upstanding guide surface may be formed adjacent the outer end of one of the arms with the guide surface extending into the groove in the other guide arm. The guide surface may, thus, reduce the size of a portion of the groove in the other guide arm to form an opening for the doubled band.

The barrel of the measuring apparatus may include an axial bore with a rod positioned within the bore. The rod may have an outer end which is secured to inner ends of the doubled band while an inner end of the rod is secured to the rotatable sleeve. To prevent rotational movement of the rod, a swivel connection may be provided between the sleeve and rod. Axial movement may, then, be transmitted from the sleeve to the rod without rotational movement of the rod.

To prevent rotation of the rod, at least a portion of the axial bore in the barrel of the apparatus may have a configuration which is complementary to the outer surface of the rod such that the rod cannot rotate within the bore. In addition, the guide means for the measuring apparatus may be curved to permit positioning of the closed loop over a tooth in a human patients mouth without undue pressure of the guide means against the inner tissue of the patients facial area or cheeks.

To secure the inner ends of the doubled band, a slide block may be slidably positioned within the guide means with the inner ends of the doubled band secured to the slide block. The rod may then be releasably secured at its outer end to the slide block with movement of the rod being transmitted to the slide block and to the doubled band to cause expansion or contraction of the closed loop in response to axial movement of the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS To illustrate the invention in terms of a preferred embodiment thereof, reference is made to the accompanying drawings in which:

FIG. 1 is a perspective view of a tooth measuring apparatus inserted into the mouth of a patient with a closed loop carried by the nose of the apparatus placed about a tooth of the patient to measure its circumference',

FIG. 2 is a side sectional view of the tooth measuring apparatus with the elements of the apparatus positioned to provide a relatively large closed loop for measuring a tooth with a large circumference;

FIG. 3 is a side view of the tooth measuring apparatus with its elements in the position shown in FIG. 2;

FIG. 4 is a side sectional view of the tooth measuring apparatus, similar to FIG. 2, in which the elements of the apparatus are positioned to provide a relatively small closed loop for measuring the circumference of a small tooth;

FIG. 5 is a side view of the tooth measuring apparatus with its elements positioned to provide a small loop at the nose of the apparatus;

FIG. 6 is an exploded view of the tooth measuring apparatus showing the component elements of the apparatus in a separated condition;

FIG. 7 is an enlarged sectional view taken along line 7-7 of FIG. 4 to illustrate the manner in which the control rod for the apparatus may be held against rotational movement, and

FIG. 8 is a sectional view taken along line 8-8 of FIG, 5 to illustrate the opening for the apparatus with a doubled band positioned within the opening to form a closed loop.

DETAILED DESCRIPTION FIG. 1 illustrates a tooth measuring apparatus 2 having a rotatable sleeve 4 in threadable engagement with a barrel 6 having guide arms 8 supported at one end of the barrel. At the extremities of guide arms 8 is formed a closed loop 10 positioned about a tooth 12 within a mouth area 14 to measure the circumference of the tooth. The guide arms 8 may be bent at a bend line 16 from axis 17 of the apparatus 2. By being bent, the guide arms 8 may, thus, be inserted within the mouth area 14 without discomfort to the patient through application of undue pressure against the inner surface of the patients cheek.

Indicia 18 are marked on barrel 6 while indicia 19 are also marked on the rotatable sleeve 4. The indicia 18 indicate the axial position of the sleeve 4 with respect to barrel 6 while indicia 19 indicate the rotational posi tion of the sleeve with respect to the barrel. The size of closed loop 10 is directly related to the position of the sleeve 4 with respect to barrel 6. Thus, the circumference of the tooth 12, as measured by loop 10, may be read directly from indicia l8 and 19.

Arrow 20 depicts rotation of the sleeve 4 in a clockwise direction to move the sleeve axially outward to contact loop 10 about the tooth 12. When the loop 10 has been contracted about tooth 12, the circumference of the tooth may be read directly from indicia 18 and 19 and the loop may then be loosened for removal from tooth 12 by rotation of the sleeve 4 in a direction opposite to arrow 20.

Turning to FIG. 2, which is a side sectional view of the tooth measuring apparatus 2, the guide arms 8 are mounted at the forward end of barrel 6 by pivot pins 22 and the arms are held together by contact of a tightening member 28 with tightening surfaces 24 on the arms. The tightening member 28 is in threaded engagement with exterior threads 26 on the barrel 6. Thus, by rotation of tightening member 28, the arms 8 may be rotated together to occupy the fixed position shown in FIG. 2. By loosening the tightening member 28, guide arms 8 may be loosened for separation through rotation of the arms about their respective pivot pins 22.

Grooves 30 and 32 are formed in the separate guide arms 8 with the grooves cooperating to form a passage between the arms when the arms are in the closed position shown in FIG. 2. A slide block 34 is positioned within the passage formed by grooves 30 and 32 and the slide block is connected to inner ends 35 of a doubled band 36. The doubled band 36 may, for example, be formed of thin metal and may have a height of about 0.150 inches. The height of the doubled band 36 permits the inner surface of the band at the closed loop 10 to lie against a substantial portion of the tooth being measured. Thus, if the tooth has an irregular exterior surface, the greatest circumferential distance about the tooth will determine the extent of the opening in the closed loop 10 as required for the loop to pass over the tooth. The height of the doubled band 36, thus, assures that the opening in closed loop 10 will measure the greatest circumferential distance about the tooth.

The use of a measuring band, such as doubled band 36, is far superior to the use of wires as previously used in the measuring of teeth. When a wire is used to measure a tooth, the wire may not be positioned about the maximum circumferential measurement of a tooth having an irregular exterior surface. When this occurs, the circumferential distance measured by the wire is incorrect.

A guide shoe 38 on the inner surface of one of the guide arms 8 may extend into the groove, such as groove 32, in the opposing face of the other guide arm. This reduces the size of the groove 32 and forms a narrowed opening 40 between the arms 8. The doubled band 36 passes through opening 40 and emerges at a nose portion 42 of the measuring apparatus 2 to form the closed loop 10.

The rotatable sleeve 4 is threadedly engaged with external threads 44 on barrel 6. The threads 44 are preferably cut very accurately such that the axial move ment of sleeve 4 during its rotation is both uniform and accurate. A bore 46 formed in barrel 6 contains a rod 48 whose outer end is releasably connected to guide block 34 through a pin connection 49. As indicated, the bore 46 may be constricted to form a sized opening 50 whose configuration prevents rotation of rod 48 with respect to the barrel 6. Thus, for example, the sized opening 50 may have a square configuration with the outer surface of rod 48 having a square configuration such that the rod is held against rotation with respect to barrel 6.

The pin connection 49 permits easy replacement oi the slide block 34 and doubled band 36. In replacing the band 36, the arms 8 are simply rotated apart by loosening tightening member 28 and the slide block 34 is disconnected from rod 48 at the pin connection 49.

External threads 52 formed at the outer end of rotatable sleeve 4 are in threaded engagement with a lock nut 54 and a rod support member 56. The rod support member 56 includes a bore 58 surrounding the rod 48 with the rod having a spherical head 60 which is held within a spherical seat 62 in the support member. The support member 56 also includes internal threads 61 which threadedly engage external threads on a cap 64.

A spherical recess 66 is formed on the leading surface of cap 64 with the recess and seat 62 coacting to form a spherical cavity for retention of spherical head 60. The spherical head 60 transmits axial movement to the rod 48 on axial movement of the sleeve 4. However, rotation is permitted between seat 62 and head 60 such that the rotation of sleeve 4 does not cause rotation of the rod 48.

FIG. 3 illustrates the position of rotatable sleeve 4 with respect to barrel 6 when the opening formed by the closed loop 10 is relatively large. As described previously, the axial movement of sleeve 4 is transmitted to the rod 48 which causes a corresponding movement of the slide block 34 and doubled band 36. The movement of doubled band 36 is directly related to the size of the opening formed by the closed loop 10. Thus, the circumference of the tooth measured by closed loop 10 may be read directly from the indicia on barrel 6 and sleeve 4.

Preferably, indicia are formed on opposite sides of the barrel 6 such that the circumferential distance measured by closed loop 10 may be read from either side of the barrel. In FIG. 3, which illustrates the opposite side of the barrel 6 shown in FIG. 1, indicia 18' on the barrel indicate the axial position of the sleeve 4 with respect to the barrel. The indicia formed on the opposite side of the barrel 6 are indicated as 18 in FIG. 1.

During one rotation of sleeve 4 with respect to the barrel 6, the sleeve will move through an axial distance that is determined by the pitch of the external threads 44 on the barrel. The indicia 19 positioned uniformly about the circumference of sleeve 4 indicate the rotational position of the sleeve to divide the axial movement of the sleeve during one rotation into a number of incremental parts as determined by the spacing of indicia 19. A reference line 21' on barrel 6 is the reference point for reading the indicia 19. Thus, in determining the axial position of sleeve 4 and the circumfer ential distance measured by closed loop 10, the circumferential distance is the sum of the measure indicated by indicia 18' and indicia 19. As indicated in FIG. 3, when closed loop 10 defines a relatively large opening, as required for measurement ofa large tooth, the sleeve 4 is moved axially toward the guide arms 8.

FIG. 4, which is a side sectional view similar to FIG. 2, illustrates the positioning of the various elements of the tooth measuring apparatus 2 when the opening defined by closed loop 10 is relatively small. As indicated, the sleeve 4 has been moved axially away from the guide arms 8 and locking member 28. This axial movement is transmitted directly to rod 48, to the slide block 34 and to the doubled band 36. This causes a reduction in the opening of the closed loop 10 as required for in FIG. 4 to provide a closed loop 10 having a small 6 opening. The opposite side of the measuring apparatus 2 is shown in FIG. 5 to demonstrate the manner in which the circumferential distance may be read on elther side of barrel 6. Conveniently, the indicia on the opposite sides of the barrel are designed to indicate the circumferential distance in millimeters which is measured by the closed loop 10. To distinguish the indicia on one side of the barrel 6 from the indicia on the other side of the barrel, the indicia on one side may be of one color while those on the other side may be a different color.

FIG. 6 is an exploded view of the tooth measuring apparatus 2 which illustrates the component parts making up the apparatus. As illustrated, guide arms 8 are each retained within a slot 68 formed in the barrel 6 with the arms retained within the slot through contact with the pivot pins 22. The end of the rod 48 which is connected to slide block 34 may be relieved at 70 with a correspondingly relieved portion 74 being formed on the slide block. The relieved portions of the rod 48 and slide block 34 may then fit together smoothly with the pin 49 engaging a hole 76 in the slide block.

FIG. 7, which is an enlarged sectional view taken along line 7-7 of FIG. 4, illustrates the manner in which rod 48 may be prevented from rotating with respect to barrel 6. As indicated, the sized opening 50 in barrel 6 may have a square configuration which is complementary to a square configuration of the rod 48. This prevents the rotation of rod 48 with respect to the barrel 6.

FIG. 8, which is a sectional view taken along line 8-8 of FIG. 5, illustrates the narrowed opening 40 formed between the guide arms 8. As indicated, guide shoe 38 extends into the groove 32 to reduce the free space within the groove in providing the narrowed opening 40. The opening 40 is sized to permit sliding movement of the doubled band 36 through the opening with the portions of the doubled band being held in face-to-face relation while passing through the open- Depending on the placement and numbering of indicia 19 on the sleeve 4, two sets of indicia 19 may be placed on the sleeve. One set of indicia 19 may be in one color, such as black, to indicate reading with the position line 21 or 21 of the same color. The other set of indicia 19 may then be of a different color, such as red, for reading with the position line 21 or 21 which is colored red.

We claim:

1. An apparatus for measuring the circumference of a tooth, said apparatus comprising:

a barrel;

a sleeve rotatably positioned about said barrel and in threaded engagement therewith;

guide means positioned at a forward end of said barrel;

a doubled band slidably positioned within said guide means;

said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop;

means connecting said band and said sleeve to transmit axial movement of said sleeve to said band without transmitting rotational movement of said sleeve to said band;

indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel;

the movement of said sleeve in a forward axial direction toward said guide means enlarging said closed loop while movement of said sleeve in a rearward axial direction away from said guide means contracts said closed loop, and

said indicia having an increasing numerical designation as said sleeve is moved in a forward axial direction toward said guide means and a decreasing numerical designation as said sleeve is moved in a rearward direction away from said guide means with the numerical designation of said indicia corresponding to the enlargement and the contraction of said loop in response to movement of said sleeve,

whereby the size of said closed loop may be varied by rotation of said sleeve with respect to said barrel with the size of said loop being indicated by said indicia which denote the axial and rotational position of said sleeve with respect to said barrel.

2. The apparatus of claim 1 wherein said guide means is curved to permit the positioning of said loop over a tooth in a human patients mouth-without undue pressure of the guide means against the inner tissue of the patients facial area.

3. The apparatus of claim 1 including a slide block slidably positioned within said guide means, and

said doubled band having inner ends secured to said slide block.

4. The apparatus of claim 1 wherein said barrel is sufficiently long to permit axial movement of said sleeve through a distance to vary the size of said loop to fit the entire size range of human teeth.

5. An apparatus for measuring the circumference of a tooth, said apparatus comprising:

a barrel;

a sleeve rotatably positioned about said barrel and in threaded engagement therewith;

guide means positioned at a forward end of said barrel;

a doubled band slidably positioned within said guide means;

said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop;

said guide means including a pair of guide arms each having an inner end pivotally connected to the forward end of said barrel for pivotal movement of said arms away from each other to an open position;

interior guide surfaces for said doubled band defined on opposed portions of said guide arms; releasable means to fix the position of said arms in a closed position with the opposed portions of said arms in contacting relation and said doubled band slidably retained within said interior guide surfaces;

means connecting said band and said sleeve to transmit axial movement of said sleeve to said band, and

indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel,

whereby the size of said closed loop may be varied by rotation of said sleeve with the size of said loop being indicated by said indicia.

6. The apparatus of claim 5 wherein said interior guide surfaces include a groove formed on each of said opposed portions,

and

said grooves forming an enclosed guide passage for said doubled band with said arms in a closed position.

7. The apparatus of claim 6 including outer ends on said arms;

an upstanding guide surface formed adjacent the outer end of one of said arms;

said guide surface extending into the groove in the other of said arms, and

said guide surface reducing the size of a portion of the groove in the other of said arms with said reduced size portion forming the said opening for said doubled band.

8. The apparatus of claim 5 wherein each of said guide arms is curved to permit the positioning of said loop over a tooth in a human patients mouth without undue pressure of said guide arms against the inner tissue of the patients facial area.

9. The apparatus of claim 5 including a slide block slidably retained within said interior guide surfaces with said arms in a closed position, and

said doubled band having inner ends secured to said slide block,

whereby movement of said slide block causes movement of said doubled band in expanding or contracting said closed loop.

10. An apparatus for measuring the circumference of a tooth, said apparatus comprising:

a barrel;

a sleeve rotatably positioned about said barrel and in threaded engagement therewith;

guide means positioned at a forward end of said barrel;

a doubled band slidably positioned within said guide means;

said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop;

an axial bore in said barrel;

a rod positioned within said bore;

said rod having an outer end secured to inner ends of said doubled band and an inner end secured to said sleeve;

a swivel connection between said sleeve and said rod to transmit axial movement of said sleeve to said rod, and

indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel,

whereby the size of said closed loop may be varied by rotation of said sleeve with the size of said loop being indicated by said indicia.

11. The apparatus of claim 10 wherein said bore and said rod have a configuration which prevents rotational movement of said rod with respect to said bore.

12. The apparatus of claim 10 including a slide block slidably positioned within said guide means;

said doubled band having inner ends secured to said slide block, and

said rod having its outer end releasably secured to said slide block. 

1. An apparatus for measuring the circumference of a tooth, said apparatus comprising: a barrel; a sleeve rotatably positioned about said barrel and in threaded engagement therewith; guide means positioned at a forward end of said barrel; a doubled band slidably positioned within said guide means; said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop; means connecting said band and said sleeve to transmit axial movement of said sleeve to said band without transmitting rotational movement of said sleeve to said band; indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel; the movement of said sleeve in a forward axial direction toward said guide means enlarging said closed loop while movement of said sleeve in a rearward axial direction away from said guide means contracts said closed loop, and said indicia having an increasing numerical designation as said sleeve is moved in a forward axial direction toward said guide means and a decreasing numerical designation as said sleeve is moved in a rearward direction away from said guide means with the numerical designation of said indicia corresponding to the enlargement and the contraction of said loop in response to movement of said sleeve, whereby the size of said closed loop may be varied by rotation of said sleeve with respect to said barrel with the size of said loop being indicated by said indicia which denote the axial and rotational position of said sleeve with respect to said barrel.
 2. The apparatus of claim 1 wherein said guide means is curved to permit the positioning of said loop over a tooth in a human patient''s mouth without undue pressure of the guide means against the inner tissue of the patient''s facial area.
 3. The apparatus of claim 1 including a slide block slidably positioned within said guide means, and said doubled band having inner ends secured to said slide block.
 4. The apparatus of claim 1 wherein said barrel is sufficiently long to permit axial movement of said sleeve through a distance to vary the size of said loop to fit the entire size range of human teeth.
 5. An apparatus for measuring the circumference of a tooth, said apparatus comprising: a barrel; a sleeve rotatably positioned about said barrel and in threaded engagement therewith; guide means positioned at a forward end of said barrel; a doubled band slidably positioned within said guide means; said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop; said guide means including a pair of guide arms each having an inner end pivotally connected to the forward end of said barrel for pivotal movement of said arms away from each other to an open position; interior guide surfaces for said doubled band defined on opposed portions of said guide arms; releasable means to fix the position of said arms in a closed position with the opposed portions of said arms in contacting relation and said doubled band slidably retained within said interior guide surfaces; means connecting said band and said sleeve to transmit axial movement of said sleeve to said band, and indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel, whereby the size of said closed loop may be varied by rotation of said sleeve with the size of said loop being indicated by said indicia.
 6. The apparatus of claim 5 wherein said interior guide surfaces include a groove formed on each of said opposed portions, and said grooves forming an enclosed guide passage for said doubled band with said arms in a closed position.
 7. The apparatus of claim 6 including outer ends on said arms; an upstanding guide surface formed adjacent the outer end of one of said arms; said guide surface extending into the groove in the other of said arms, and said guide surface reducing the size of a portion of the groove in the other of said arms with said reduced size portion forming the said opening for said doubled band.
 8. The apparatus of claim 5 wherein each of said guide arms is curved to permit the positioning of said loop over a tooth in a human patient''s mouth without undue pressure of said guide arms against the inner tissue of the patient''s facial area.
 9. The apparatus of claim 5 including a slide block slidably retained within said interior guide surfaces with said arms in a closed position, and said doubled band having inner ends secured to said slide block, whereby movement of said slide block causes movement of said doubled band in expanding or contracting said closed loop.
 10. An apparatus for measuring the circumference of a tooth, said apparatus comprising: a barrel; a sleeve rotatably positioned about said barrel and in threaded engagement therewith; guide means positioned at a forward end of said barrel; a doubled band slidably positioned within said guide means; said guide means including an opening with the portions of said doubled band which extend beyond the opening forming a closed loop; an axial bore in said barrel; a rod positioned within said bore; said rod having an outer end secured to inner ends of said doubled band and an inner end secured to said sleeve; a swivel connection between said sleeve and said rod to transmit axial movement of said sleeve to said rod, and indicia on said barrel and sleeve to denote the axial and rotational position of said sleeve with respect to said barrel, whereby the size of said closed loop may be varied by rotation of said sleeve with the size of said loop being indicated by said indicia.
 11. The apparatus of claim 10 wherein said bore and said rod have a configuration which prevents rotational movement of said rod with respect to said bore.
 12. The apparatus of claim 10 including a slide block slidably positioned within said guide means; said doubled band having inner ends secured to said slide block, and said rod having its outer end releasably secured to said slide block. 